Question

seja a PA ( 20 ,17 , 14 ...........) calcule o decimo termo ou a10

Answer 1

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$a_n=a_{-10}=? \\ a_1=20 \\ n=10 \\ r=17-20=-3 \\ \\ a_n=a_1+(n-1)r \\ \\ a_{10}=20+(10-1)(-3) \\ \\ a_{10}=20+9(-3) \\ \\ a_{10}=20-27 \\ \\ a_{10}=-7$